The present invention relates to fibrous web structures suitable for absorbing discharged body fluids and to absorbent gelling agent compositions especially useful in these structures. Such structures can be incorporated into disposable absorbent articles such as sanitary napkins, infant diapers, adult incontinence pads and the like.
Absorbent structures which comprise entangled masses of fibers, i.e., fibrous webs, are well known in the art. Such structures can imbibe liquids, such as discharged body fluids, both by an absorption mechanism wherein fluid is taken up by the fiber material itself and by a wicking mechanism wherein fluid is acquired by, distributed through and stored in the capillary interstices between fibers. One means for improving the absorbency characteristics of such fibrous web structures is to incorporate therein so-called superabsorbent polymers which imbibe fluid to thereby form a swollen hydrogel material. The resulting hydrogel serves to retain fluid such as discharged body liquids within the structure. An absorbent structure of this type wherein hydrogel-forming materials in particulate (including fiber) form are incorporated into fibrous webs is disclosed in Weisman and Goldman; U.S. Pat. No. 4,610,678; issued Sept. 9, 1986.
The size and configuration of particle-form hydrogel-forming polymers (i.e., gelling agents) incorporated into absorbent structures can vary widely. The above-cited U.S. Pat. No. 4,610,678, for example, indicates that gelling agent particles incorporated into such absorbent structures can range in size from about 30 microns to about 4 mm. In actual commercial practice, however, the particles of gelling agent employed in absorbent cores for disposable diapers are frequently irregular but not highly elongated in configuration, range in particle size from about 45 to 850 microns and have a mass median particle size of from about 200 to 370 microns. Particles of this shape and size are generally selected because of industrial hygiene and ease-of-processing considerations.
Some commercially available gelling agent materials are furthermore produced in the form of particles which are agglomerates of smaller particles since the larger agglomerates are easier to handle in gelling agent synthesis and packaging operations. It is believed, however, that agglomerates of this type break down to some degree during their incorporation into disposable absorbent articles manufactured in commercial operations and during subsequent use of such articles. Products of this type such as diapers thus may actually contain gelling agent in the form of particles that are somewhat smaller than the gelling agent agglomerates originally provided in raw material form for diaper-making operations.
Whatever the size and form of gelling agent particles employed in known absorbent structures, the gelling agent is generally more expensive than the staple fiber component which forms the principal part of the structure. Accordingly, the materials, configurations and processing used in making such absorbent structures are often manipulated and adjusted in order to maximize the absorbent capacity of the absorbent structure and the effective absorbent capacity of the gelling agent material employed in the structure. In this manner, the minimum amount of gelling agent consistent with the realization of desired absorbent performance objectives can be used. This, in turn, tends to minimize the cost of producing the absorbent structure.
Given the fact that there is a continuing need to improve absorbent structure absorbency characteristics, it is an objective of the present invention to provide a type of absorbent structure configuration wherein structure absorbent capacity and effective capacity of the gelling agents therein can be improved.
It is a further object of this invention to provide such absorbent structures of improved absorbent capacity and gelling agent efficiency by the simple adjustment and control of particle size distribution of the gelling agent materials employed in the absorbent structure.
It is a further object of the present invention to provide gelling agent compositions which have controlled particle size characteristics and which are especially suitable for incorporation into such absorbent structures.
It is a further object of the present invention to provide disposable absorbent articles such as diapers, training pants, incontinence pads, sanitary napkins and the like, which utilize such absorbent structures of improved absorbency characteristics to form their absorbent cores.